Field of the Invention
The present invention relates to a friction stir welding member.
Discussion of the Background
There is a known Friction Stir Welding technique that is a technique for welding a steel plate to an aluminum plate (for example, see FIG. 2 in Japanese Unexamined Patent Application Publication No. 2006-239720).
Japanese Unexamined Patent Application Publication No. 2006-239720 is described with reference to the following figures.
FIG. 15 is a diagram illustrating the basic principle of the conventional art. In the Friction Stir Welding technique, a second member 202 with material properties different from those of a first member 201 is stacked thereon, and a pin 204 of a welding tool 203 which is rotated in a direction indicated by an arrow (1) is inserted into the second member 202. The welding tool 203 is relatively moved with the end of the pin 204 located at a height of h3 from the surface of the first member 201 that faces the second member.
Frictional heat is generated between the rotating pin 204 and the second member 202, and causes the second member 202 to be softened. The softened member 202 solidifies to become a welded portion 208, which serves to weld the second member 202 to the first member 201. Consequently, the second member 202 is welded to the first member 201, and a friction stir welding member 205 is obtained.
The length of the welded portion 208 may be set to be less than the length of the second member 202 in accordance with a design instruction, a work execution instruction, or the like. A cross-sectional view in this case is described in the following.
FIG. 16 is a cross-sectional view of a conventional friction stir welding member. A hole 206 is formed through the second member 202 after the pin 204 of the welding tool 203 is removed, and a surface 207 of the first member 201 that faces the second member is externally exposed. The first member 201 is a metal with a low voltage, the second member 202 is a metal with a high voltage, and thus if water comes into the hole 206 of the second member 202 and reaches the surface 207 of the first member 201 that faces the second member, a current flows from the second member 202 to the first member 201 via the water. Then the surface 207 that faces the second member corrodes due to the current.
As a way of preventing this corrosion, the hole 206 of the second member 202 may be blocked by a blocking member, however, this increases the production time because of the additional time required to attach the blocking member to the hole 206.
As another solution to this problem, the hole 206 may be filled with the second member 202 that is softened (softened material). In order to fill the hole 206 with the softened material, the pin 204 is pulled out from the softened material in FIG. 15, and a tool main body 209 is rotated as indicated by an arrow outline with a blank inside and is extruded to the softened material. By extruding the tool main body 209, the softened material is pressed by the tool main body 209. The pressed softened material flows into the hole which is then filled with the softened material.